Blogging can help a site improve its ranking, visibility, and community.

When it comes to indexing, it isn't that uncommon for search engines spiders to ignore parts of a site -- particularly if a site has hundreds or thousands of pages.  At times, site owners don't want pages indexed, but there are a fair share of those out there who are frustrated that some pages are ignored by search spiders. 

Sitemaps can help improve deep pages' visibility, but blogging can help as well.  If a site has a blog, the posts can contain relevant links to pages deep within a site.  Since search engines do spider blogs, such links can help lure the spiders to index these pages.  Further, such links can introduce blog readers to these pages that they may not typically navigate to, since they are so deep within the site's structure and they may link to such a page if it was helpful and/or interesting to them.  However, it is important to only link to pages with valuable nuggets of information that are worth attention from spiders and humans alike.  

Constantly updated blogs are also useful to attract spiders more often to a site since new content is produced frequently.  Such updates also beckon interested web surfers who desire fresh information about whatever the site is about.  Also, blogs can also serve as linkbait, which can help improve a site's ranking and visibility.

What are other SEO benefits of blogs?  What are some SEO drawbacks?